In packing machines of the type described above, the conveyor pockets are filled, as they travel along the loading path, by operating the pushers in a succession of cycles. At each cycle, all the pushers are operated once in an operating sequence in which the time lapse between operation of two consecutive pushers equals the time taken for the conveyor to advance a number of steps, which may even be zero, and which depends on the pair of pushers considered and may vary from one pair to another.
Though widely used for forming groups of cigarettes on packing machines, the above method has several drawbacks, mainly due to any faulty groups, i.e. incomplete groups or groups containing one or more faulty cigarettes, being rejected from the respective pockets downstream from the group-forming station.
As a result of the vacancy produced along the conveyor by rejection of a faulty group, the packing materials relative to the missing group must also be rejected, thus possibly resulting in jamming of the packing machine. To eliminate this drawback, complex, high-cost control systems have been proposed to detect a vacancy travelling along the packing machine, and to prevent supply of the relative packing materials accordingly.